Syringes used for delivery of medicaments are principally constructed of a barrel and a stopper. The stopper is slidably fitted within the syringe barrel and may have a stopper rod affixed to it for actuation of the syringe and delivery of medicament. The stopper is generally constructed of an elastomer, with silicone oil applied. The silicone oil is applied to reduce sliding friction between the stopper and barrel and to improve the seal between them. The oil allows for ease of sliding when administering a dose which may ensure the full dose can be administered. Partial dosing is of particular concern in the case of pens and so-called auto injecting syringes. In such applications the oil is also critical to prevent jamming of the device which can lead to trauma at the site of injection. The improved sealing provided by silicone oil also may ensure that no foreign contaminants like bacteria enter the syringe.
Recently there has developed a trend favoring pre-filled syringes which function to both store and deliver medicaments. Such pre-filled syringes may offer cost savings to the pharmaceutical industry and may improve safety, convenience and efficacy of medicament delivery. Biopharmaceuticals are an important class of pharmaceuticals that may increase the use of pre-filled syringes and related devices (pens, auto injectors and the like). Such biopharmaceuticals may include insulin, vaccines, antibodies, blood products, hormones, cytokines, and the like. As more pharmaceuticals and particularly biopharmaceuticals utilize delivery in pre-filled syringe and similar devices, the challenges of conventional syringe technology become apparent.
Several aspects of traditional syringe construction present a challenge for their use as pre-filled syringes. The use of silicone oil is a concern, because the oil may degrade the medicament and because a small amount of silicone may be injected with it. The oil is may also be of particular concern with regard to biopharmaceuticals because it may cause aggregation of certain proteins.
Another issue that arises in prefilled syringes is that the elastomer of the stopper may contain leachable and extractable contaminants. These may also contaminate the medicament upon long term storage in syringes. Trace amounts of residual monomer or plasticizer or other impurities from the stopper can adversely effect the therapeutic or can have an adverse impact on the patient once injected.
Among the many other considerations affecting prefilled syringe devices and similar devices and their components are the need to be sterilized, stability with transport and storage for up to a few years, optical clarity, the need to integrate into existing filling equipment (including the durability requirements for stopper cleaning and insertion into the syringe barrel), leachables and extractables of all components of the syringe, and the need to maintain sterility from filling through administering of the contents, and finally user preferences and ergonomic considerations. For a variety of reasons the prefilled syringe market uses both glass and plastic barrels.